One known surgical technique for correcting intervertebral disc damage or degeneration (and associated instability of the spinal column) involves surgically removing damaged disc material and fusing the vertebrae immediately above and below the damaged disc. In one form, this can be achieved by inserting, anteriorly, a piece or pieces of bone to promote bone grafting in the intervertebral space that previously was occupied by the damaged disc. In another form, this can be achieved by inserting a metallic prosthesis which is so configured and surface-treated such that, when fixed in position between the intervertebral space, new bone growth is more likely to occur. Examples of the latter include the Titan Endoskeleton® suite of devices.
The insertion of bone for the purpose of promoting fusion between adjoining vertebrae may be accompanied by positioning a rigid (e.g. metal) plate across the graft area of the intervertebral disc space and by securing the plate by screws to the anterior face of the vertebrae immediately above and below the graft area. The plate can provide immediate stability to the spinal column at the treated level and can facilitate fusion of the bone graft.
A difficulty with the fusing technique is that anatomical mobility, including rotation at the treated intervertebral level, is not possible. Further, as the number of vertebrae that are fused together increases, the mobility and rotation of the spine is correspondingly reduced. Also, the fusing of two or more vertebrae in this manner may result in increased wear on the discs immediately above and below those which are fused, and this can result in accelerated breakdown of and damage to the discs immediately above and below the fused section. This consequential damage may lead to pain and discomfort for a patient and possibly to further corrective surgery. The rigidness created by fusing a portion of the spinal column, which by nature and function should remain flexible, is not entirely satisfactory. However, it is recognized that in some patients, depending on the extent of their diagnosed intervertebral disc degeneration and or disease, fusing of the vertebrae may be the only surgical option.
Another known surgical technique for correcting intervertebral disc damage or degeneration involves an artificial disc replacement (ADR) device. ADR technologies have been developed to correct or otherwise treat degenerate disc disease (DDD) more effectively and/or as an alternative to fusing techniques. ADR devices are intended to maintain spinal mobility within the normal range of spinal movement and to reduce the incidence of degeneration of discs at adjacent segments of the spine.
Again, the ADR devices are designed to be surgically implanted anteriorly into the intervertebral space between two adjoining vertebrae following surgical removal of the damaged or diseased disc material. The ADR device is intended to function anatomically like a natural disc, ideally maintaining mobility and stability of the spine, and acting ideally as a shock absorber between the vertebrae.
ADR devices that provide for total disc replacement may be composed of metal plates (e.g. titanium, cobalt, chrome) with or without component elements, including materials such as polyethylene, polyurethane, plastics, ceramics, polymers, injectable fluids, hydrogels and elastic coils.
ADR devices are subjected to stringent clinical testing because, among other causes of failure, some ADR devices have been known to dislocate from the intervertebral space between vertebrae.
Examples of spinal disc implants (ADR devices) are shown in each of WO03057088, U.S. Pat. No. 7,066,960, US2009112326, WO2008088869 and KR20100116331.
WO2008088869 discloses a mesh-based spinal implant. Polymer may be moulded around the mesh.
U.S. Pat. No. 7,066,960 discloses a disk prosthesis including a matrix of bio-compatible fabric that is impregnated in its central region with a liquid or semi-liquid polymer to form a nuclear core (nucleus) of the prosthesis.
US2009112326 discloses a spinal implant having first and second flanges, each extending in opposite directions from an intermediate body that comprises upper and lower facing, spaced portions that combine to define an interior in the implant.
WO03057088 discloses a spinal disc implant which comprises an enclosure for insertion into a disc space between two adjacent vertebrae. The enclosure surrounds and supports a plurality of elongated members in the form of polymer rods or tubes.
KR20100116331 discloses an intervertebral cervical spinal implant that has a protruding member extending from a body of the device. However, the protruding member has an annular shape and thereby defines a hollow interior. As a result, saw-tooth projections from upper and lower surfaces of the protruding member are required to abut and interface with the two adjacent vertebrae. KR20100116331 is actually concerned with variable directional fasteners.
The above references to the background prior art do not constitute an admission that such art forms a part of the common and/or general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the device and procedure as disclosed herein.